An aliphatic polyester, such as polyglycolic acid or polylactic acid, can be decomposed by microorganisms or enzymes present in nature, such as soil or sea water, and is therefore noted as a biodegradable polymer material giving little load to the environment. Further, an is aliphatic polyester has degradability and absorbability in vivo, so that it is used also as a polymer material for medical use, such as sutures for surgery or artificial skin.
Among the aliphatic polyesters, polyglycolic acid is excellent in gas barrier properties, such as oxygen gas barrier property, carbon dioxide gas barrier property and water vapor barrier property, and also is excellent in heat resistance and mechanical properties, and therefore the development of new use thereof by itself or as a composite material together with another resin material, is under way.
However, aliphatic polyesters, inclusive of polyglycolic acid, are generally hydrolyzable and accompanied with a problem that the barrier property and strength are impaired along with the hydrolysis.
In melt-processing of aliphatic polyester resins including polyglycolic acid, various phosphoric or phosphorous acid esters are incorporated for improving thermal properties, such as melt stability and crystallinity (Patent document 1 listed below). (Herein, the term “phosphoric or phosphorous acid ester” is used to collectively refer to at least one of phosphoric acid esters and phosphorous acid esters.) However, it is difficult to regard that the resultant aliphatic polyester resin composition has been effectively improved in moisture resistance.    Patent document 1: WO2003/037956A1